Releasable coupling devices, including fluid-actuated releasable fasteners, which are responsive to remote controlled operation are used in a variety of operating environments. For aerospace applications, wherein the potential for catastrophic failure has imposed a continuing need for increasing the reliability of such devices, mechanically two fault tolerant systems have been devised to provide redundant release means. Mechanically two fault tolerant systems, which employ three latch pins that are retractable from a toggle latching member, are shown in U.S. Pat. Nos. 4,864,910 and 4,836,081. Such systems, however, have design load limits relating to the bending stress of the pins. It has been found that unexpected large tensile forces applied at the separation plane of the coupling systems, can permanently deform the pins such that the "bent" pins may not retract and therefore lead to a failure in separating. Other disadvantages are that the three pin layout design requires considerable use of space in the plane perpendicular to the preload vector, which space requirement increases as the demand for preload increases. The preloading on the pins induces high friction forces making the pins harder to retract and requiring greater retraction forces. Also, valuable area on the piston face needed for application of pressure to retract a pin is taken up by the shaft of the pin.
In U.S. Pat. No. 4,682,804 there is disclosed a release mechanism for spacecraft wherein a pair of locking surfaces engage opposite sides of a pivoted pawl tab. The mechanism is one fault tolerant in that if only one of the locking surfaces be released, the panel tab pivots to release the other surface. The prior art also includes releasable fasteners which are zero fault tolerant in that failure of any one component results in a failure to release. Since such zero fault tolerant and one fault tolerant systems do not provide the degree of redundancy inherent in a two fault tolerant system they are therefore less desirable for many aerospace applications.